Question

Space charge region around a p-n junction:
A. Does not contain mobile carriers
B. Contains both free electrons and holes
C. Contains one type of mobile carriers depending on the level of doping
D. Contains electrons only as free carriers

Answer 1

Hint: The space charge region around a p-n junction is also called the depletion region.

Complete step by step answer:
The space charge region around a p-n junction is also called the depletion region. It is formed due to electrons from the n-side occupying the holes of the p-side and vice versa on both sides of the junction to create a small space of net charge neutrality. This process depletes the space charge region around the p-n junction of any free mobile charge carriers. This is the reason why this region is also called the ‘depletion region’.
This region actually contains equal amounts of a fixed positively charged region and a fixed negatively charged region on the n and p sides of the junction respectively. This takes care of the neutrality of charge and also sets up a barrier potential in the semiconductor.
This process of formation of depletion region and barrier potential is actually quite important from the perspective of many of the properties and uses of p-n junction diodes and transistors.
Thus, the space charge region around a p-n junction does not contain mobile carriers.
Hence, the correct option is A) Does not contain mobile carriers.

Note: Semiconductor physics can be quite confusing and may require a good number of readings for a proper grasp and understanding of the concepts. It is imperative that the student correctly understands the construction of diodes and transistors and their properties, since many questions are usually based on them.
A student could have easily gotten confused as to whether holes are considered mobile carriers or not in this question and made a mistake.